This Background section is provided for informational purposes only, and does not constitute and admission that any of the subject matter contained herein qualifies as prior art to the present application.
Mass spectrometry (MS) is among the most informative of analytical techniques. Due to its combination of speed, selectivity, and sensitivity MS has wide ranging applications in areas such as trace elemental analysis, biomolecule characterization in highly complex samples, and isotope ratio determination. However, the large size, weight, and power consumption (SWaP) found in some MS systems generally limits analyses to the laboratory setting. Applications for which rapid measurements in the field are desirable or where in-lab analyses are not optimal would benefit from the development of hand portable, miniaturized MS systems.
Much of the SWaP and complexity in MS operation lies in the vacuum systems necessary to attain the high vacuums needed for most mass analyzers (10−5-10−9 torr). Accordingly, one approach to SWaP reduction is the ability to perform MS at higher pressures. Ion traps may be operated at pressures greater than 10−4 torr so may be used as mass analyzer for miniature systems. However, in some cases, increasing pressures in an ion trap significantly above a few millitorr has a deleterious effect on resolution and signal intensity. The increasing number of collisions with the buffer gas at higher pressures inhibits the ability of the electric field to control the ions' trajectory. Increasing the operating frequency (typically a radio frequency or “RF”) of the trap yields fewer neutral collisions per cycle, reducing the negative effects of high pressure operation but may require a corresponding decrease in trap dimensions in order to reduce the required RF voltage amplitude.